FR3129688A1 - Management of the operation of an exhaust catalyst of an internal combustion engine - Google Patents

Abstract

Method for managing the operation of an exhaust catalyst of an internal combustion engine, said method comprising the following steps: - determination of the maximum oxygen storage capacity (OSC) of the catalyst considered, - determination for each cylinder of the engine and at each combustion cycle of a quantity of oxygen, in excess or in deficiency, introduced into the exhaust line from the quantity of air and the quantity of fuel introduced into the cylinder considered and parameters engine operation, - from the previous determination, iterative determination of the quantity of oxygen present in the catalyst, this quantity being between 0 and the maximum oxygen storage capacity of the catalyst considered, and - determination of injection instructions for a combustion cycle to come as a function of the quantity of oxygen present in the catalyst and of engine operating parameters. Abstract Figure: Figure 3

Description

Management of the operation of an exhaust catalyst of an internal combustion engine

This disclosure relates to the management of the operation of an exhaust catalyst of an internal combustion engine. More generally, this disclosure relates to the treatment of exhaust gases in motor vehicle engines, and more particularly to the purging of oxygen in a motor vehicle exhaust catalyst, for example during an injection recovery .

The present disclosure finds applications, in particular, in engine control systems for motor vehicles equipped with direct fuel injection engines.

It is known that a motor vehicle internal combustion engine, whether it is a spark ignition engine (known as a gasoline engine) operating with gasoline as fuel or a compression ignition engine (known as Diesel engines) operating with diesel as fuel, generates polluting gases resulting from the combustion of the corresponding air-fuel mixture in one or more cylinders of the engine. These polluting gases include in particular unburned hydrocarbons (or HC), carbon monoxide (CO) and nitrogen oxides (NOx, set for NO which designates nitrogen monoxide and for NO2 which designates nitrogen dioxide ). HC and CO are produced, essentially, following incomplete combustion of the fuel, generally due to a lack of oxygen in the mixture, and this phenomenon affects gasoline engines more than diesel engines. Benefiting from a more complete combustion, a diesel engine is indeed more affected by the emission of NOx.

In order to limit the release of these polluting gases into the atmosphere, it is now common to equip the exhaust system of a gasoline-powered motor vehicle with a catalytic converter or exhaust catalyst. A three-way exhaust catalyst can treat the three pollutants identified above (i.e. HC, CO, and NOx) at once. The function of the exhaust catalyst is to reduce pollution in the environment by reducing or destroying the polluting gases resulting from the imperfect combustion of the air-fuel mixture in the engine cylinders, thanks to a chemical reaction of catalysis. For a gasoline engine, the exhaust catalyst converts CO and NO2 into a non-polluting substance. For a diesel engine, the exhaust catalyst converts CO and HC into carbon dioxide and water. The exhaust catalyst is effective at high temperatures, which is why it is placed very close to the engine in order to heat up and quickly reach its ideal operating temperature.

The efficiency of the treatment in the catalyst is maximum at richness 1, that is to say at richness equal to unity, that is to say for a gas-oxygen mixture which respects the stoichiometric proportion. This follows directly from the conservation laws of nature, i.e. the conservation of atoms and the conservation of the electrical charges of atoms during molecular transformations resulting from chemical reactions in the exhaust catalyst.

A mixture is said to be lean (its richness is less than 1) if it contains an oxygen content higher than the stoichiometric proportion and it is said to be rich if it contains an oxygen content lower than the said stoichiometric proportion. The ideal mixture is 14.7g of oxygen for 1g of fuel (for gasoline), also called "stoichiometric mixture". It allows to generate a homogeneous and complete combustion, weakly polluting. It also makes it possible to ensure the best efficiency of the engine resulting in lower consumption, to the detriment, however, of power. Indeed, obtaining maximum power requires a rich mixture. A "lambda" coefficient, measured by a probe of the same name and conventionally represented by the corresponding Greek letter (λ), making it possible to determine the wealth. This coefficient is the inverse of wealth as expressed in the manner indicated above. In other words, the ratio is ideal when lambda=1, while the mixture is lean if lambda>1 and rich if lambda<1. The maximum power of the engine is obtained with a rich dosage and is around lambda=0.86.

Regulations in force throughout the world, in particular the European emission standards known as "Euro standards", set maximum authorized limits for the discharge of polluting gases by new vehicles, with the aim of reducing atmospheric pollution due to road transport. These "Euro standards" follow one another, being numbered in an increasing way, and differ between the various types of engines and vehicles but the constant tendency is that they are more and more strict. In order to comply with these ever more restrictive standards, it is obviously necessary to improve the performance of the engines in all the operating phases of the motor vehicles, in order to obtain the maximum mechanical power with the minimum fuel consumed. However, this is not enough. It is also necessary to improve the efficiency of the exhaust gas pollution control systems with which the vehicle is fitted, in particular the exhaust catalyst, taking account in particular of the variation in engine speed and the variable composition of exhaust gases. resulting exhaust.

For example, when the injection in the engine of a motor vehicle is cut off, which may be the result of a vehicle deceleration command by the driver, the engine sends fresh air into the exhaust catalyst, i.e. air not mixed with fuel. The exhaust catalyst then takes on oxygen (O ₂ ). When injection is resumed, the mixture in the catalyst is therefore still relatively lean, due to the portion of this oxygen remaining in the exhaust catalyst. Under these conditions, the HC and the CO are well consumed by the exhaust catalyst but the NOx are not 100% treated. All this lasts for the time that the exhaust catalyst returns to richness 1, due to the progressive consumption of oxygen in this catalyst, i.e. the time to purge the excess oxygen accumulated in the catalyst exhaust during the injection cut-off.

The document FR3107085 discloses a process for purging oxygen, on resumption of injection, in a motor vehicle exhaust catalyst equipped with an internal combustion engine with direct injection and controlled ignition, comprising the injection of exhaust gasoline, in at least one cylinder and for at least one four-stroke cycle of said cylinder during the exhaust phase of said cycle, in response to the determination of a resumption of injection terminating an engine operating sequence with injection cut-off.

This document of the prior art provides a solution for quickly consuming the oxygen in the catalyst when the mixture in the catalyst is lean and thus makes it possible to limit the duration during which this mixture is lean. Thus, polluting emissions are limited since the catalytic converter returns to its optimum operating conditions more quickly.

Summary

This disclosure further improves the situation. It aims to further improve the efficiency of the operation of an exhaust catalyst in the context of purging oxygen which has accumulated in an exhaust catalyst, for example following a cut-off of injection following a vehicle deceleration command by its driver.

To this end, a method is proposed for managing the operation of an exhaust catalyst of an internal combustion engine having at least one cylinder and an exhaust line integrating said catalyst, said method comprising a step for determining the maximum oxygen storage capacity of the catalyst under consideration.

According to the present disclosure, this method further comprises the following steps:
- determination for each cylinder of the engine and at each combustion cycle of a quantity of oxygen, in excess or in deficiency, introduced into the exhaust line from the quantity of air and the quantity of fuel introduced into the cylinder considered and engine operating parameters,
- from the previous determination, iterative determination of the quantity of oxygen present in the catalyst, this quantity being between 0 and the maximum oxygen storage capacity of the catalyst considered, and
- determination of injection instructions for a combustion cycle to come as a function of the quantity of oxygen present in the catalyst and of engine operating parameters.

According to this method, the quantity of oxygen present in the catalyst is known. We determine here for each cylinder and each engine cycle (with or without combustion), on the one hand, the quantity of oxygen introduced into the exhaust line and, on the other hand, the quantity of fuel introduced into this exhaust line. 'exhaust. By taking the balance, the method determines each time (that is to say per cylinder and for each corresponding cycle in a so-called four-stroke engine with two revolutions -or 720°- of rotation of the crankshaft) whether oxygen is sent in excess or in default in the exhaust line compared to a stoichiometric mixture. It is thus possible to iteratively know the quantity of oxygen present in the catalyst. If oxygen is sent in excess into the exhaust line, it will be added to the oxygen already present in the catalyst within the limit (known or predetermined) of the maximum storage capacity of this catalyst and if oxygen is sent by default into the exhaust line, the oxygen contained in the catalyst will be consumed, thus reducing the quantity of oxygen present in the catalyst, this quantity obviously not being able to be negative. The fact then of knowing in real time the quantity of oxygen in the catalyst makes it possible to best adapt the quantity of unburned fuel to be introduced into the exhaust line so that it reacts in the exhaust catalyst with the oxygen present there. The engine operating parameters must be taken into account here to determine the quantity of unburned fuel to be introduced into the exhaust line because it is necessary in particular to ensure that the conditions are met for the exhaust catalyst to be able to carry out the desired chemical reaction.

The features set out in the following paragraphs can optionally be implemented, independently of each other or in combination with each other:

- to determine the quantity of oxygen introduced into the exhaust line, for a cycle during which fuel is injected into the cylinder considered, a theoretical quantity of excess or lacking oxygen is calculated from a value of setpoint of a lambda value corresponding to the inverse of the richness of the air/fuel mixture entering the cylinder, and said theoretical value corresponds to the product of the mass of air introduced into the cylinder with the oxygen concentration of this mass d air and with the difference between the lambda setpoint value and the lambda setpoint value corresponding to combustion not supplying oxygen to the exhaust;

- to determine the quantity of oxygen introduced into the exhaust line, for a cycle during which fuel is injected into the cylinder considered, a corrective quantity of excess or deficient oxygen is calculated from a value of filtered setpoint of a lambda value corresponding to the inverse of the richness of the air/fuel mixture entering the cylinder, and said corrective value corresponds to the product of the mass of air introduced into the cylinder and the oxygen concentration of this mass of air and with the difference between the filtered lambda setpoint value and the measured lambda value;

- to determine the quantity of oxygen introduced into the exhaust line, for a cycle during which fuel is injected into the cylinder considered, a quantity of oxygen consumed is calculated from a mass of fuel injected at the exhaust, that is to say injected in such a way that it does not burn and passes directly into the exhaust line, and said value of oxygen consumed corresponds to the mass of oxygen necessary to carry out combustion of said mass of fuel under stoichiometric conditions;

- to determine the quantity of oxygen introduced into the exhaust line for a cycle during which fuel injection is deactivated, said quantity of oxygen is calculated by multiplying the mass of air introduced into the cylinder by the concentration of oxygen from that air mass;

- the injection instructions can include either the injection of fuel into the cylinder to achieve combustion and produce an engine torque, or the injection of fuel into the exhaust then the injection of fuel into the cylinder to achieve combustion , either the injection of fuel into the exhaust without injection of fuel to achieve combustion, or a cutoff of the injection;

- the following parameters are taken into account to determine the injection instructions: the exhaust catalyst is being heated, the temperature of the exhaust catalyst, the quantity of oxygen present in the exhaust catalyst, the gradient of said quantity of oxygen, the flow in the exhaust line and the maximum oxygen storage capacity of the exhaust catalyst.

According to another aspect, a computer program is proposed comprising instructions for the implementation of a method presented above when this program is executed by a processor, in particular a processor of an electronic control unit of an engine internal combustion.

According to another aspect, there is provided a non-transitory recording medium readable by a computer on which is recorded a program for the implementation of a method presented above when this program is executed by a processor.

Brief description of figures

Other characteristics, details and advantages will appear on reading the detailed description below, and on analyzing the appended drawing, on which:

Fig. 1

is a simplified diagram of a direct injection internal combustion engine, with its supply means and with its exhaust line, to which the embodiments of the invention can be applied.

Fig. 2

is a diagram, in section, of a cylinder of the engine of the .

Fig. 3

is an overall block diagram of a process for managing the operation of the catalyst of the according to one embodiment of the present disclosure.

Fig. 4

shows in more detail a step of the process of the .

Fig. 5

shows in more detail another step in the process of the .

The present technical solutions can be applied in particular to the management of the operation of an exhaust catalyst.

Knowing the oxygen remaining in the catalyst in real time makes it possible to better manage its consumption and to optimize it for, from a situation where the mixture present in the catalyst is lean (excess oxygen) , quickly arrive at a situation in which the richness of the mixture in the catalyst is equal to 1.

The proposed solution also makes it possible to take into account the aging of the exhaust catalyst and thus to optimize the treatment of NOx and CO over the entire life of the catalyst.

The present disclosure thus participates in further limiting the polluting emissions of an engine by allowing the exhaust catalyst of an engine to work again under optimal conditions when the mixture within the catalyst no longer has a richness of 1, after a injection cut-off for example.

This disclosure is not limited to the preferred exemplary embodiment and the variants mentioned above, solely by way of example, but it encompasses all the variants that a person skilled in the art may consider in the context of the protection sought.

Claims (9)

Method for managing the operation of an exhaust catalyst (12) of an internal combustion engine (1) having at least one cylinder (3) and an exhaust line (11) incorporating said catalyst, said method comprising a step of determining the maximum oxygen storage capacity (OSC) of the catalyst in question,
characterized in that it further comprises the following steps:
- determination for each cylinder (3) of the engine and at each combustion cycle of a quantity of oxygen, in excess or in deficiency, introduced into the exhaust line (11) from the quantity of air and the quantity of fuel introduced into the cylinder (3) considered and engine operating parameters,
- from the previous determination, iterative determination of the quantity of oxygen present in the catalyst, this quantity being between 0 and the maximum oxygen storage capacity (OSC) of the catalyst considered, and
- determination of injection instructions for a combustion cycle to come as a function of the quantity of oxygen present in the catalyst and of engine operating parameters. Management method according to Claim 1, characterized in that to determine the quantity of oxygen introduced into the exhaust line (11), for a cycle during which fuel is injected into the cylinder (3) in question, a theoretical quantity excess or lacking oxygen is calculated from a setpoint of a lambda value corresponding to the inverse of the richness of the air/fuel mixture entering the cylinder (3), and
in that said theoretical value corresponds to the product of the mass of air introduced into the cylinder (3) with the oxygen concentration of this mass of air and with the difference between the set value of lambda and the set value of lambda corresponding to a combustion not supplying oxygen to the exhaust. Management method according to one of Claims 1 or 2, characterized in that to determine the quantity of oxygen introduced into the exhaust line (11), for a cycle during which fuel is injected into the cylinder (3) considered, a corrective quantity of excess or lacking oxygen is calculated from a filtered set point value of a lambda value corresponding to the inverse of the richness of the air/fuel mixture entering the cylinder (3), And
in that said corrective value corresponds to the product of the mass of air introduced into the cylinder (3) with the oxygen concentration of this mass of air and with the difference between the filtered lambda set point value and the lambda value measured. Management method according to one of Claims 1 to 3, characterized in that to determine the quantity of oxygen introduced into the exhaust line (11), for a cycle during which fuel is injected into the cylinder (3) considered, a quantity of oxygen consumed is calculated from a mass of fuel injected at the exhaust, that is to say injected in such a way that it does not burn and passes directly into the exhaust line (11), and
in that said value of oxygen consumed corresponds to the mass of oxygen necessary to carry out combustion of said mass of fuel under stoichiometric conditions. Management method according to one of Claims 1 to 4, characterized in that to determine the quantity of oxygen introduced into the exhaust line (11) for a cycle during which the fuel injection is deactivated, the said quantity of oxygen is calculated by multiplying the mass of air introduced into the cylinder (3) by the oxygen concentration of this mass of air. Management method according to one of Claims 1 to 5, characterized in that the injection instructions can comprise either the injection of fuel into the cylinder (3) to carry out combustion and produce an engine torque, or the injection of fuel to the exhaust then the injection of fuel into the cylinder to achieve combustion, or the injection of fuel to the exhaust without injection of fuel to achieve combustion, or a cutoff of the injection. Management method according to one of Claims 1 to 6, characterized in that the following parameters are taken into account to determine the injection instructions: the exhaust catalyst (12) is being heated, the temperature of the catalyst exhaust pipe (12), the quantity of oxygen present in the exhaust catalyst (12), the gradient of said quantity of oxygen, the flow rate in the exhaust line (11) and the maximum storage capacity in (OSC) from the exhaust catalyst (12). Computer program comprising instructions for implementing the method according to one of Claims 1 to 7 when this program is executed by a processor, in particular a processor of an electronic control unit of an internal combustion engine. Non-transitory recording medium readable by a computer on which is recorded a program for implementing the method according to one of Claims 1 to 7 when this program is executed by a processor.